1. Field of the Invention
The present invention relates to magnetic sensors in which a fixed magnetic layer is provided at least one side surface of a free magnetic layer in a track width direction with a non-magnetic material layer provided therebetween and in which current flows in a direction intersecting an interface between the free magnetic layer and the non-magnetic material layer and an interface between the fixed magnetic layer and the non-magnetic material layer. More particularly, the present invention relates to a magnetic sensor which can increase the rate of change in resistance.
2. Description of the Related Art
In recent years, concomitant with improvement in recording density of recording media, a decrease in the gap length which is defined by the distance between a top and a bottom shield has been increasingly required. The top and bottom shield are made of a magnetic material and are provided on the top and the bottom of a magnetic sensor.
As a major structure of a reproduction magnetic head reading a signal magnetic field from a recording medium, a spin-valve type magnetic sensor has been widely used in which a free magnetic layer and a fixed magnetic layer are laminated to each other perpendicularly to the film surface with a non-magnetic material layer interposed therebetween.
However, in the structure in which a free magnetic layer, a non-magnetic material layer, and a fixed magnetic layer are laminated to each other perpendicularly to the film surface, it becomes difficult to further decrease the gap length.
Accordingly, a magnetic sensor having the following structure has been proposed in which fixed magnetic layers are provided on two side surfaces of a free magnetic layer with non-magnetic material layers provided therebetween, and in which current flows in the direction intersecting each interface between the free magnetic layer and the non-magnetic material layer and each interface between the fixed magnetic layer and the non-magnetic material layer.
FIG. 14 is a partial cross-sectional view of a magnetic sensor 1, when it is viewed from a face opposing a recording medium, in which a sense current flows in the direction intersecting the interfaces described above. In the magnetic sensor 1, a free magnetic layer 5 in the form of approximately trapezoid, which is made of a soft magnetic material such as NiFe, is formed above a lower shield layer 2 made of a magnetic material with a lower gap layer 3 of an insulating material and an underlying layer 4 provided therebetween. On the two side surfaces of the free magnetic layer 5 and on the lower gap layer 3, non-magnetic material layers 6 are formed. In addition, fixed magnetic layers 7 made of a soft magnetic material such as NiFe are formed in contact with the respective non-magnetic material layers 6. Antiferromagnetic layers 8 are provided on the respective fixed magnetic layers 7, an exchange coupling magnetic field is generated at each of interfaces between the fixed magnetic layers 7 and the antiferromagnetic layers 8, and the magnetizations of the fixed magnetic layers 7 are fixed in a Y direction in the figure. On the free magnetic layer 5 and the antiferromagnetic layers 8, an upper gap layer 9 made of an insulating material and an upper shield layer 10 made of a magnetic material are formed.
A sense current of the magnetic sensor 1 described above flows in the fixed magnetic layers 7, the non-magnetic material layers 6, and the free magnetic layer in the direction intersecting the interfaces between the fixed magnetic layers 7 and the non-magnetic material layers 6 and the interfaces between the non-magnetic material layers 6 and the free magnetic layer 5 (X direction in the figure).
The free magnetic layer 5 is placed in a single domain state in the X direction in the figure, and when an external magnetic field is applied in the Y direction in the figure, the magnetization of the free magnetic layer 5 is rotated in the Y direction in the figure. While the magnetizations of the fixed magnetic layers 7 are fixed in the Y direction in the figure, when the magnetization of the free magnetic layer 5 is rotated, the resistance of the magnetic sensor is changed. When this change in resistance is read as the change in current or the change in voltage, an external magnetic field can be detected.
Magnetic sensors as described above are disclosed, for example, in U.S. Pat. Nos. 6,396,668B1 and 6,411,478B1, and Japanese Unexamined Patent Application Publication No. 2001-319313 (p.6, FIG. 2). A magnetic sensor disclosed in U.S. Pat. No. 6,396,668B1 is a spin-valve type GMR element, and magnetic sensors disclosed in U.S. Pat. No. 6,411,478B1 and Japanese Unexamined Patent Application Publication No. 2001-319313 are tunneling MR elements.
In the magnetic sensor 1 shown in FIG. 14, a sense current flows in the direction intersecting the interfaces between the fixed magnetic layers 7 and the non-magnetic material layers 6 and the interfaces between the non-magnetic material layers 6 and the free magnetic layer 5. Accordingly, it has been believed that the change in resistance by application of an external magnetic field to the magnetic sensor 1 is primarily caused by bulk scattering of conduction electrons of the sense current in the free magnetic layer 5 and the fixed magnetic layer 7. Hence, in the magnetic sensor 1, a larger change in resistance can be obtained as compared to a related current-in-plane type magnetic sensor in which the change in resistance is caused by scattering of sense current electrons at an interface between a free magnetic layer and a non-magnetic material layer or primarily at an interface between the non-magnetic material layer and a fixed magnetic layer. In addition, since the fixed magnetic layer 7 is not provided on the top or the bottom of the free magnetic layer 5, which is a position for detecting a magnetic field, the distance between the top and the bottom shields of the free magnetic layer 5 can be decreased, and hence the decrease in gap can be achieved.
In a magnetic sensor having the structure shown in FIG. 14, when the free magnetic layer 5 and the fixed magnetic layers 7 are not formed to have a large thickness to a certain extent, diffusive scattering of conduction electrons having a longer free mean path (majority electrons, such as, up-spin conduction electrons) quickly occurs at the top or the bottom surfaces of the free magnetic layer 5 and the fixed magnetic layers 7, and as a result, the spin diffusion length (movable distance of electrons while the spin state thereof is maintained) is decreased. Consequently, the change ΔR in resistance is decreased, and a problem in that the reproduction output cannot be increased may arise in some cases.
On the other hand, when the thicknesses of the free magnetic layer 5 and the fixed magnetic layers 7 are increased, the problem described above can be solved; however, since a magnetic moment per unit area of the free magnetic layer 5 is increased, the sensitivity is decreased. In addition, since the exchange coupling magnetic field between the fixed magnetic layer 7 and the antiferromagnetic layer 8 is also decreased, a magnetization fixing force for the fixed magnetic layer 7 is decreased, and as a result, a problem in that the MR properties are degraded may arise.
Accordingly, for example, the structure of a magnetic sensor 1A shown in FIG. 15 has been proposed in which the free magnetic layer 5 is formed to have a synthetic ferrimagnetic structure composed of a first free magnetic material layer 5a, a second free magnetic material layer 5b, and a non-magnetic intermediate layer 5c interposed therebetween for solving the problems such as the decrease in reproduction sensitivity.
However, when the structure shown in FIG. 15 is formed, the following problems occur. For example, as shown in FIG. 15, the first free magnetic material layer 5a and the second free magnetic material layer 5b are magnetized in a direction to the left in the figure (as shown by the arrow) and in a direction to the right in the figure (as shown by the arrow), respectively, and the fixed magnetic layers 7 are magnetized in a height direction (Y direction in the figure). In the case in which an external magnetic field enters the magnetic sensor along the Y direction, when the magnetization of the first free magnetic material layer 5a is rotated in the Y direction shown in the figure, and the magnetization of the second free magnetic material layer 5b is rotated in a direction opposite to the Y direction shown in the figure, a magnetization direction of the first free magnetic material layer 5a and that of the fixed magnetic material layer 7 decrease the resistance, and on the other hand, a magnetization direction of the second free magnetic material layer 5b and that of the fixed magnetic material layer 7 increase the resistance. Hence, the changes in resistance are cancelled out, and as a result, a high rate of change in resistance cannot be obtained. When the fixed magnetic layer 7 is formed to have a synthetic ferrimagnetic structure as described above, the same problems as described above occur.